This Small Grant (R03) proposal for a new investigator is in response to PA-99-002's objective number 7 focusing on studying substance use among special populations. This application to the National Institute on Drug Abuse proposes 2 years of support for research on substance use and dependence among uninsured U.S. household residents using data from the National Household Survey on Drug Abuse (NHSDA). The proposed research requires no new and costly data gathering. Secondary data analysis will be performed on 1995-1996 NHSDA data. Despite the increasing number of the uninsured documented in the U.S. and its associated adverse consequences, no studies systematically estimate the extent and the magnitude of substance abuse service needs of a national sample of the uninsured. The major goals of the study are to provide recent national estimates of the prevalence for substance use, heavy use, and dependence problems, and to identify high-risk subgroups of the uninsured in need of prevention, intervention, and/or treatment of tobacco, alcohol, and other drug use problems. The specific aims of the proposed study are as follows: (1) to provide population estimates of substance use, heavy use, and dependence by social and demographic characteristics among the uninsured; (2) to determine which class of substance use is associated with an increased likelihood of substance dependence among those who have used the substance in the past year; (3) to understand the correlates of substance cessation, continued use but not dependence, and substance dependence among those who have ever used the substance; and (4) to examine whether the co-occurrence of mental health problems increases the likelihood of having substance dependence and the use of treatment. Findings from the proposed analysis have significant implications. They will (a) provide population estimates on the scope and the magnitude of substance use and dependence problems for the uninsured; (b) identify subgroups of the uninsured who have an increased likelihood of substance use, heavy use, or dependence problems so they can be targeted for early prevention and intervention; (c) specify subgroups of the uninsured who may be adversely affected by both substance use and mental health problems and are in need of treatment services; (d) provide vital information for predicting the potential future burden of substance use problems among the uninsured as well as for policymaking and the planning of treatment services for substance-abusing individuals; and (e) for further research, identify gaps in our knowledge of substance use problems among the uninsured.